GROUP C

PROPAGATION OF EVENTS IN PROGRESS

The time evolution of large Solar Energetic Particle (SEP) events shows a great deal of variability in such features as the initial rise of intensity, time of maximum intensity, and decay times. When multiple events take place, as is often the case for the most active periods, these features may overlap with preceding events. In addition the passage of interplanetary shocks at Earth orbit often adds an additional increase in intensity. The maximum intensities and distribution of particles with different energies also vary widely. Finally, the relative numbers of highly ionizing heavy nuclei vary greatly in different events. All these complex features are related to the acceleration mechanisms and subsequent propagation of energetic particles in interplanetary space. Only by understanding the physical mechanisms operating in these events will it be possible to successfully predict likely outcomes.

This group will discuss current research in this area including observations and advances in modeling. Examples of current research questions in this area are:

What is the longitudinal extent of SEP acceleration along the shock?
How does the shock connect magnetically to Earth?
What are the causes of high-energy (>30 MeV/nucleon) variability in SEPs?
Why are some events rich in heavy nuclei such as Fe?
Do the flanks and nose of the shock accelerate particles with the same spectrum?
How do the maximum flux and fluence vary with distance from the Sun?
How can one predict when there will be a large shock spike such as in the one in October 1989?
What kind of data is need to improve acceleration models and how can one incorporate these models into global models describing shock propagation and CMEs?
What determines when there will be a rapid time to maximum (e.g., Jan 20, 2005) and when there will be a gradual time to maximum (e.g., October 28, 2003)?
Do "streaming limits" really work?
What new models and observations are needed?